Effect of portal glucose sensing on systemic glucose levels in SD and ZDF Rats

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Abstract

BACKGROUND: The global epidemic of Type-2-Diabetes (T2D) highlights the need for novel therapeutic targets and agents. Roux-en-Y-Gastric-Bypass (RYGB) is the most effective treatment. Studies investigating the mechanisms of RYGB suggest a role for post-operative changes in portal glucose levels. We investigate the impact of stimulating portal glucose sensors on systemic glucose levels in health and T2D, and evaluated the role of sodium-glucose-cotransporter-3 (SGLT3) as the possible sensor. METHODS: Systemic glucose and hormone responses to portal stimulation were measured. In Sprague-Dawley (SD) rats, post-prandial state was simulated by infusing glucose into the portal vein. The SGLT3 agonist, alpha-methyl-glucopyranoside (alphaMG), was then added to further stimulate the portal sensor. To elucidate the neural pathway, vagotomy or portal denervation was followed by alphaMG+glucose co-infusion. The therapeutic potential of portal glucose sensor stimulation was investigated by alphaMG-only infusion (vs. saline) in SD and Zucker-Diabetic-Fatty (ZDF) rats. Hepatic mRNA expression was also measured. RESULTS: alphaMG+glucose co-infusion reduced peak systemic glucose (vs. glucose alone), and lowered hepatic G6Pase expression. Portal denervation, but not vagotomy, abolished this effect. alphaMG-only infusion lowered systemic glucose levels. This glucose-lowering effect was more pronounced in ZDF rats, where portal alphaMG infusion increased insulin, C-peptide and GIP levels compared to saline infusions. CONCLUSIONS: The portal vein is capable of sensing its glucose levels, and responds by altering hepatic glucose handling. The enhanced effect in T2D, mediated through increased GIP and insulin, highlights a therapeutic target that could be amenable to pharmacological modulation or minimally-invasive surgery.

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Pal, A., Rhoads, D. B., & Tavakkoli, A. (2016). Effect of portal glucose sensing on systemic glucose levels in SD and ZDF Rats. PLoS ONE, 11(11). https://doi.org/10.1371/journal.pone.0165592

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